1. Field of the Invention
The present invention relates to lubrication systems for internal-combustion engines and, more particularly, to lubrication systems for such engines and turbochargers.
2. Description of the Prior Art
Workers in the art of internal-combustion engines have long tried to minimize wear on the engines. For example, substantial efforts have been made to improve lubricants for the engines, and to provide improved bearings and lubrication systems.
It is well known in the automotive art that wear in automobile and other vehicle engines of the internal-combustion type is not simply related to the number of miles driven, but depends upon the conditions under which the vehicle is driven. For example, it is recognized that an engine of a vehicle which is utilized for frequent short trips will wear faster (on a per-mile basis) than the engine of a vehicle which is driven less frequently but longer distances. This difference in wear life can be explained, at least in part, by the fact that friction is at its maximum value during the first few minutes after a cold engine is started and that, after the engine has warmed to its normal operating temperature, friction within the engine drops substantially. Some workers in the automotive art have estimated that up to ninety percent (90%) of the total mechanical wear of an engine occurs within a relatively short time after starting the engine cold. In one article on this subject, workers in the art estimated that an automobile engine undergoes the same amount of mechanical wear during the first thirty seconds after it is started cold as the engine would undergo if driven fully warm for five hundred miles. In otherwords, according to this source, the wear during a thirty second cold start of an engine may equal approximately the wear undergone by a fully warm engine over a nine hour period of normal operation. Similarly, The Society of Automotive Engineers has determined that up to eighty percent of the wear on vehicle engines occurs during the first ten seconds of operation. Accordingly, it is clear that critical times for engine wear occur during the period that the engine is being cranked by the starter motor and before the mechanical oil pump of the engine has had sufficient time to fill the oil galleys of the engine with oil at the normal operating pressure.
To overcome such frictional wear during cold starting of an automobile engine, prior art workers have provided reservoir systems which are filled and pressurized with oil while the engine is operating and which hold the oil under pressure during the period the engine is off, and then release the oil to the engine just as the engine is restarted. The difficulty with such reservoir systems is that relatively high pressures are required and leakage normally occurs during the period that the engine is off, thereby causing the pressurized reservoir system to lose its effectiveness.
Similar pressurized reservoir systems have been employed with engines equipped with turbochargers. The wear associated with typical turbochargers normally occurs because, after an engine is shut off, the turbocharger may continue to rotate at 75,000 to 5,000 rpm for a period of time after the mechanical oil pump for the engine has been shut off. To prevent undue wear of the rotating parts of the turbocharger, it has been proposed to utilize a pressurized oil reservoir of the type described above which discharges to the turbocharger whenever the engine is shut off, and then is recharged after the engine begins operation.